Proceedings of the International Conference on Mechanical Engineering 2009 (ICME2009) 26- 28 December 2009, Dhaka, Bangladesh ICME09-AM-12 © ICME2009 1 AM-12 1. INTRODUCTION Fiber reinforced polymer matrix composites due to their high specific strength and specific stiffness to weight ratios have become attractive structural materials in aerospace industry, marine, armor, automobile, railways, civil engineering structures, sport goods etc. [1]. The incorporation of inorganic fillers has proved to be an effective way of improving the mechanical and thermal properties of these materials. However, the typical filler content needed for significant enhancement of these properties can be as high as 10-20% by volume. The processing of the materials often becomes difficult at such high particle volume fractions due to the higher density of the inorganic filler than the resin and the increased density of the filled resin [2]. In this rationale, nanoparticles such as CNFs, CNTs, clay, metallic nanoparticles filled fiber reinforced polymer matrix composites are attracting considerable attention since they can enhance properties that are sometimes even higher than the conventional filled polymers composites at volume fractions in the range of 1 to 5%. Improvements in mechanical, electrical, and chemical properties have resulted in major interest in nanocomposite materials in numerous automotive, aerospace, electronics and biotechnology applications. These nanoscale materials provide the opportunity to explore new behavior and functionality beyond those found in conventional materials. It has been established that the addition of small amounts of nanoparticles (<5 wt. %) to a matrix system can increase thermal and mechanical properties without compromising the weight or process-ability of the composite [3]. The higher surface area is one the most promising characteristics of the nanoparticles due to its ability of creating a great interface in a composite. An interphase of 1 nm thick represents roughly 0.3% of the total volume of polymer in the case of micro particle filled composites; whereas it can reach 30% of the total volume in the case of nanocomposites [4]. Contribution made by the interphase modified by the low nanofiller loading provides possibilities of enhanced performance by reinforced composites with a small percentage of strong fillers can significantly improve the mechanical, thermal, and barrier properties of the pure polymer matrix [6]. Choi et al. [7] have fabricated and studied the Epoxy/CNF composite with different proportions of CNFs by the in situ process modifying both low and high viscous epoxies. The SEM images showed a high level of dispersion for all materials, although occasional small aggregates were observed in high viscosity epoxy of 20 wt%. The storage modulus and T g of the polymer were increased by incorporation of CNFs. The results showed the maximum tensile strength and Young’s modulus at 5 wt% of CNF and reduction of the fracture strain with increasing filler content. Mechanical, electrical and thermal properties of low viscosity epoxy composites were resulted better than that of the high viscosity composites. Hussain et al. [8] have investigated the effect of nanoscale Al 2 O 3 particles in filament wound carbon fiber/epoxy composites and found an increase in modulus, flexural strength, MECHANICAL AND THERMAL CHARACTERIZATION OF CNF- FILLED POLYESTER NANOPHASED COMPOSITE Mohammad Kamal Hossain, Muhammad Enayet Hossain, Mahesh Hosur and Shaik Jeelani Tuskegee University, Tuskegee, USA ABSTRACT A high intensity ultrasonic liquid processor was used to infuse carbon nanofibers (CNFs) into polyester matrix which was then mixed with catalyst using a high speed mechanical agitator. Results showed the significant improvement in the dispersion of CNFs in sonication over the mechanical mixing method. Flexure tests performed on the neat polyester (NP), 0.1wt. %, 0.2 wt.%, 0.3 wt.% and 0.4 wt.% CNF- filled polyester (CNF-FP) showed 86% and 16% increase in flexural strength and modulus, respectively, compared to the unfilled polyester with increasing loading percentage of CNF up to 0.2%. Similar trend was found with CNF-filled glass reinforced polyester (CNF-FGRP) composites manufactured by vacuum assisted resin transfer molding (VARTM). Dynamic mechanical analysis (DMA) studies indicated an increasing trend of storage modulus and glass-transition-temperature (T g ) values of all nanophased composites compared to neat polyester. Scanning electron microscopy (SEM) micrographs of fracture surfaces revealed relatively smooth surface of neat polyester compared to the nanophased polyester. Keywords: Polyester, CNF, Mechanical and Thermal Properties.